This site is supported by donations to The OEIS Foundation.



Thanks to everyone who made a donation during our annual appeal!
To see the list of donors, or make a donation, see the OEIS Foundation home page.

(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A023814 Number of associative binary operations on an n-set; number of labeled semigroups. 14
1, 1, 8, 113, 3492, 183732, 17061118, 7743056064, 148195347518186, 38447365355811944462 (list; graph; refs; listen; history; text; internal format)



Table of n, a(n) for n=0..9.

Alex Bailey, Martin Finn-Sell, Robert Snocken, Subsemigroup, ideal and congruence growth of free semigroups, arXiv preprint arXiv:1409.2444, 2014.

A. Distler and T. Kelsey, The semigroups of order 9 and their automorphism groups, arXiv preprint arXiv:1301.6023, 2013.

C. Noebauer, Home page [broken link]

C. Noebauer, The Numbers of Small Rings

C. Noebauer, Thesis on the enumeration of near-rings

Eric Postpischil Posting to sci.math newsgroup, May 21 1990

Eric Weisstein's World of Mathematics, Semigroup.

Index entries for sequences related to semigroups


Cf. A001423, A001426, A023813, A023815, A027851.

a(n) + A079172(n) = A002489(n).

Sequence in context: A072402 A092084 A099715 * A217772 A062126 A222520

Adjacent sequences:  A023811 A023812 A023813 * A023815 A023816 A023817




Lyle Ramshaw (ramshaw(AT)pa.dec.com)


a(8), a(9) from Distler and Kelsey (2013). - N. J. A. Sloane, Feb 19 2013



Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified January 19 11:47 EST 2019. Contains 319306 sequences. (Running on oeis4.)